Generalised approach to modelling a three-tiered microbial food-web

Area of Science:

• Environmental microbiology
• Biochemical engineering
• Systems biology

Background:

• Complex models like Anaerobic Digestion Model No. 1 (ADM1) are used for anaerobic digestion but are difficult to analyze for stability.
• Previous work simplified ADM1 to a three-tiered food web with Monod kinetics, finding stable steady states where all organisms coexisted.

Purpose of the Study:

• To investigate the stability of a generalized three-tiered microbial food web with non-Monod kinetics.
• To analytically characterize steady-state stability without a maintenance term and explore its dependence on operating parameters.
• To identify critical behaviors and unstable regions in microbial communities under changing conditions.

Main Methods:

• Developed a generalized food-web model applicable to various growth kinetics.
• Performed analytical stability analysis for systems without a maintenance term.
• Utilized numerical analysis for systems including a maintenance term.
• Examined the impact of parameter variations on system stability and operating diagrams.

Main Results:

• Without a maintenance term, steady-state stability can be analytically determined, revealing insights into the operating region for coexistence.
• Identified four cases demonstrating the dependence of the operating diagram on biological parameters for Monod kinetics.
• Confirmed that the washout steady-state is always stable.
• Discovered that a switch in dominance between hydrogen-competing organisms leads to instability and loss of viability.
• Reported a novel unstable operating region where all three organisms coexist in the positive steady-state.

Conclusions:

• The simplified model and analytical approach provide a better understanding of microbial food-web stability and operating regions.
• The findings highlight critical phenomena such as the stability of washout and the instability caused by competitive exclusion.
• This analysis framework can predict critical behaviors in microbial communities facing environmental changes.